Preheat oven to 425 degrees and spray two 12-cup muffin tins with baking spray or line with cupcake liners.
Combine flour, cocoa powder, baking powder, baking soda, and salt together in a medium bowl. Stir until well mixed then set aside.
2 1/2 cups flour, 1/2 cup cocoa powder, 1 TBS baking powder, 1/2 tsp baking soda, 1/2 tsp table salt
Whisk together eggs and sugar in a large bowl until smooth.
2 large eggs, 1 cup granulated sugar
Add oil, sour cream, milk, and vanilla to egg mixture. Whisk until smooth.
1 cup whole milk, 1/2 cup vegetable oil, 1/3 cup sour cream, 1 tsp vanilla extract
Pour the bowl of dry ingredients into the bowl of wet ingredients and stir carefully to combine until there are no dry patches left.
Use a 1 1/2 TBS cookie scoop to put 1 1/2 TBS of batter into the bottom of 22 of the 24 muffin cups in the prepared muffin tin.
Add 1 heaping teaspoon of Nutella on top of the batter in the cups.
22 tsp Nutella
Top with another 1 1/2 TBS of muffin batter to cover the Nutella. Sprinkle with decorator's sugar if desired.
Bake for five minutes at 425 degrees F. Lower the oven to 350 degrees (with muffins still in oven) and bake for an additional 10-13 minutes or until a toothpick comes out clean.
Let the muffins cool in the muffin tin for five minutes then remove from the tin and allow to cool on a wire rack until ready to eat.
Make them even more decadent by adding a cup of your favorite chocolate chips to the batter.Make these sweet and salty by substituting the sugar on top with a little coarse flake salt (like on these salted caramel toffee cookies) for a sweet and salty treat.Store in an airtight container at room temperature for up to four days or freeze after the four days if you haven’t eaten all of them yet (unlikely).